1. Field of the Invention
The present invention relates to a process for the preparation of foams characterized by carbodiimide and isocyanurate linkages. More particularly, the invention relates to the use of a co-catalyst system comprising a C.sub.1 -C.sub.8 alkali metal carboxylate and a carbodiimide-promoting compound in the preparation of foams characterized by carbodiimide and isocyanurate linkages.
2. Prior Art
The preparation of rigid foams characterized by carbodiimide and isocyanurate linkages is well known in the art as evidenced by inter alia U.S. Pat. Nos. 3,645,923; 3,657,161; 3,717,596; 3,723,366; and 3,746,709. Generally these foams are prepared by catalytically condensing an organic polyisocyanate in the presence of a compound which promotes the carbodiimide reaction and a compound which promotes the trimerization reaction. Representative trimerization compounds known in the art include: (a) organic strong bases, (b) tertiary amine cocatalyst combinations, (c) Friedel-Crafts catalysts, (d) basic salts of carboxylic acids, (e) alkali metal oxides, alkali metal alcoholates, alkali metal phenolates, alkali metal hydroxides and alkali metal carbonates, (f) onium compounds from nitrogen, phosphorus, arsenic, antimony, sulfur and selenium and (g) monosubstituted monocarbamic esters.